The present invention relates to a communication system between a vehicle network and a wayside network.
According to the terminology “vehicle” the invention concerns especially rail train with one or more units in which a communication means between a trainborne network and a wayside network is provided.
A first communication system is disclosed in WO200126337-A2 wherein a remote controlling of electronic components in vehicles through Internet as wayside network is provided for example for transmitting routing and security information for multimedia traffic through a device (GPS device, cellular phone, PDA, etc) connected over Wireless Local Area Network WLAN. By this way, a radio-frequency (wireless) connection from Internet to a so-called client (remote device) in the vehicle can be provided.
According to EP1071239-A1 a train network with radio frequency based network between a transmitter (=client in the train) and a receiver (=access point at the wayside) is disclosed. To secure the active transfer of information between these two stations across the network a frame is transmitted from transmitter to receiver. By non valid or absent received frame at the receiver a non-valid confirmation is sent back to the transmitter to re-iterate the initial transfer of information. By this way a loss of signal information from a broken communication path can be avoided.
Furthermore, due to the limited transmission distance as the vehicle moves, a connection based on radio-frequency transmission/reception between a client in the vehicle and one of access points of the wayside network has to be actualized in a way that avoids a loss of connection. Such a new association procedure between a client and a new access point is known as a so-called roaming function. Unfortunately, the association and the roaming processes require a time period during which a communication of a data stream is not possible.